Superconducting open MRI magnet with transverse magnetic field

Abstract

The present invention relates to magnets and to magnetic resonance imaging systems. The magnet is open with magnetic coils arranged in quadrant, separated about two perpendicular planes, a midplane and a plane of reflection, and wherein the windings are configured such that, in operation, current flow is symmetrical about the plane of reflection and anti-symmetrical about the midplane, to produce a nett magnetic field at the center in a direction perpendicular to the plane of reflection.

1. A magnet assembly comprising four sets of magnetic coils, each set of coils comprising windings of electrical conductive material; wherein:
 the sets of magnetic coils are arranged in quadrants, separated about two mutually perpendicular planes, including a midplane and a plane of reflection;  
 the sets of coils are also symmetrical about a third plane that is perpendicular to both the midplane and the plane of reflection, such that the three planes are mutually orthogonal;  
 each of the coils is wound around an axis that is perpendicular to the midplane; and  
 the windings are configured such that, in operation, current flow in said coils is symmetrical about the plane of reflection and anti-symmetrical about the midplane, whereby a resultant net magnetic field is produced at a center of the assembly in a direction perpendicular to the plane of reflection.  
 
   
   
     2. A magnet according to  claim 1 , where the magnetic coils comprise D coils. 
   
   
     3. A magnet according to  claim 1 , wherein the magnet coils comprise banana coils. 
   
   
     4. A magnet according to  claim 1 , wherein the magnet coils comprise sub-coils. 
   
   
     5. A magnet according to  claim 4 , wherein the sub-coils are provided in a nested and/or overlapping arrangement. 
   
   
     6. A magnet according to  claim 1 , wherein the coils are non-planar. 
   
   
     7. A magnet according to  claim 1 , adapted for us in a magnetic resonance imaging system. 
   
   
     8. A magnetic resonance imaging system comprising:
 a primary magnet assembly;  
 a cryostat unit; and  
 a gradient magnet assembly; wherein,  
 the primary magnet assembly comprises windings of electrical conductive material arranged in sets of coils;  
 the sets of coils are arranged in quadrants, separated about two mutually perpendicular planes, including a midplane and a plane of reflection;  
 the sets of coils are also symmetrical about a third plane that is perpendicular to both the midplane and the plane of reflection, such that the three planes are mutually orthogonal;  
 each of the coils is wound around an axis that is perpendicular to the midplane;  
 the windings are configured such that, in operation, current flow in said coils is symmetrical about the plane of reflection and anti-symmetrical about the midplane;  
 the primary magnet is situated within the cryostat to provide an operating temperature at which superconductivity is possible; and  
 the gradient magnets are operable to provide magnetic fields across predetermined planes to enable magnetic resonance imaging.  
 
   
   
     9. A system according to  claim 8 , where the magnetic coils comprise D coils. 
   
   
     10. A system according to  claim 8 , wherein the magnet coils comprise banana coils. 
   
   
     11. A system according to  claim 1 , wherein there are sub-coils. 
   
   
     12. A system according to  claim 11 , wherein the sub-coils are provided in a nested and for overlapping arrangement. 
   
   
     13. A system according to  claim 8 , wherein the coils are non-planar. 
   
   
     14. A method of operating a magnet assembly within a cryostat, the magnet assembly having a plurality of magnetic coils having windings of electrically conductive material, the magnetic coils being arranged in quadrants separated symmetrically about two mutually perpendicular planes, including a midplane and a plane of reflection, sets of coils also being symmetrical about a third plane that is perpendicular to both the midplane and the plane of reflection, such that the three planes are mutually orthogonal, and each of the coils being wound around an axis that is perpendicular to the midplane; the method comprising:
 cooling the magnet assembly to a temperature at which superconductivity is possible; and  
 flowing current in the magnetic coils such that current flow in said coils is symmetrical about the plane of reflection and anti-symmetrical about the midplane.